1. Field of the Invention
This invention relates to an apparatus and method for driving a liquid-crystal dot-matrix display for use in word processors, personal computers, and others.
2. Description of the Related Art
FIG. 1 is an overall block diagram of a conventional driving apparatus for a liquid-crystal display. A column-electrode driving integrated circuit 11 and a row-electrode driving integrated circuit 12 are connected to a dot-matrix liquid-crystal display (hereinafter, referred to as a liquid-crystal display) 10. The column-electrode driving integrated circuit 11 and row-electrode driving integrated circuit 12 are controlled by a controller 13 of a control integrated circuit.
The column-electrode driving integrated circuit 11 is composed of a shift register 11.sub.1, a latch circuit 11.sub.2, and a driving circuit 11.sub.3. The shift register 11.sub.1 is supplied with the display data D and shift clock pulse SCP that are supplied from the controller 13. The display data D is taken by the shift register 11.sub.1 at the falling edge of the shift clock pulse SCP, and shifted sequentially. The latch circuit 11.sub.2 is supplied with the latch signal LP1 from the controller 13. In response to the latch signal LP1, the latch circuit 11.sub.2 latches the display data D stored in the shift register 11.sub.1. The display data D latched in the latch circuit 11.sub.2 is supplied to the driving circuit 11.sub.3. The driving circuit 11.sub.3 converts the display data D into alternating signal form according to the converting-to-AC signal FR from the controller 13, and the resulting signal is supplied to the liquid-crystal display 10.
The row-electrode driving integrated circuit 12 is made up of a shift register 12.sub.1 and a driving circuit 12.sub.2. The shift register 12.sub.1, in response to the falling edge of the latch signal LP2 from the controller 13, takes the shift data FP from the controller 13 and shifts it sequentially. In response to the converting-to-AC signal FP from the controller 13, the shift data FP stored in the shift register 12.sub.1 is converted into alternating current form by inverting the data in polarity for each frame, and the resulting signal is supplied to the liquid-crystal display 10.
FIG. 2 is a timing chart for the liquid-crystal display with the FIG. 1 driving apparatus in a mode other than the double-height font mode, with the same parts as in FIG. 1 indicated by the same reference characters.
COL1 to COL3 represent the column-electrode driving waveforms, and ROW1 to ROW5 the row-electrode driving waveforms. Although COL1 to COL3 and ROW1 to ROW5 are actually converted into alternating signal form under the control of the converting-to-AC signal FR, COL1 to COL3 are indicated by the level 1 or 0 according to the display data D, and ROW1 to ROW5 take the 1 level (selected) or the 0 level (unselected) only, for the sake of simplification. The same signal is normally used for the latch signals LP1 and LP2.
The display data latched in the latch circuit 11.sub.2 in response to the latch signal LP1 appears at COL1 to COL3 under the control of the converting-to-AC signal FR. One line of display data is supplied to COL1 to COL3, and at the same time, a single row electrode is selected in response to the latch signal LP2, with the result that the display data appears on the liquid-crystal display 10.
FIG. 3A shows a case where numeral 5 is displayed on the liquid-crystal display 10 in accordance with the FIG. 2 timing chart.
FIG. 4 is a timing chart for the liquid-crystal display with the FIG. 1 driving apparatus in the double-height font mode that enlarges and displays the data twice in height that of the original.
In this case, the latch signal LP2 of the 1 level is supplied twice during one period of the latch signal LP1. By selecting two row electrodes sequentially during the time when a single line of display data is being supplied to COL1 to COL3, the display data with a size doubled in height appears on the display.
FIG. 3B shows a case where a numeral 5 is displayed in the double-height font mode on the liquid-crystal display 10 according to the FIG. 4 timing chart.
To display the data with a size doubled in height, the conventional driving apparatus uses two latch signals LP1 and LP2, which are supplied to the latch circuit 11.sub.2 and the shift register 12.sub.1 via separate wires, respectively. This leads to the increased number of output terminals of the controller 13, and consequently, the increased number of pins, thus making the circuitry complicated.